In this study, fine coal from the Tuncbilek Region (Turkey) was subjected to autogenous medium washing tests. The autogenous medium was formed in the presence of clayey minerals with the increased solids concentration of the feed slurry. The clayey minerals also acted as tracer to investigate the conditions of free settling conditions where the particle size based separation was observed. The effect of feed slurry, solids concentration, and the presence of clayey minerals on the separation of coal fines were investigated for the sizes of -300, -150, and -75 mu m. The results reveal that the solids concentrations lower than 10% resulted in the particle size based separation (free settling conditions) and the solids concentrations higher than 10% required the density based separations (hindered settling conditions). Satisfactory separations were achieved at solids concentrations of 10-40%. In the case of higher solids concentrations, an additional increase on separation was ascribed to the development of autogenous medium separation. In addition, the increase in the solids concentration, the presence of clayey minerals on feed also created the autogenous medium separation conditions.